The present invention relates to a switching valve, in particular for the actuation of an injection valve in an internal combustion engine, comprising a valve body in which a flow passage is formed which opens with one end into a work space, and comprising valve plate which is accommodated in the work space and which can be moved between a closure position and an opening position. The invention further relates to an injection valve with a switching valve of this kind.
A switching valve of this kind is known and is used in particular for the actuation of valves, such as for example injection valves in internal combustion engines. For this purpose the switching valve has a flow passage, the one end of which can be connected to a pressure chamber of the valve to be actuated. The other end of the flow passage opens into a work space which is provided at the switching valve and in which a valve plate is arranged for the closing off of the flow passage. The valve plate can be moved back and forth between a closure position and an opening position. Through opening of the flow passage the pressure chamber of the valve to be actuated can for example be connected to an outflow line or to the surroundings.
The known switching valve is used in an injection valve in a diesel engine in order to be able to determine the injection moment and the injection duration of the fuel to be injected through the injection valve. For the closing of the injection nozzle of the injection valve a nozzle needle is provided which is displaceably journalled in a needle guide and which is hydraulically clamped in such a manner in between the injection nozzle and the pressure chamber to which to the flow passage of the switching valve is connected that the nozzle needle holds the injection nozzle closed. Through opening of the flow passage the fluid which is located in the pressure chamber depresses so that the nozzle needle opens the injection nozzle. After the closing of the flow passage, pressure builds up again in the interior of the pressure chamber, through which the nozzle needle is again moved into its position which closes the injection nozzle.
The object of the invention is to provide a switching valve or, respectively, an injection valve with a switching valve of this kind which or, respectively, in which the switching valve is simple to manufacture and seals off the flow passage correctly with simple means.
This object is satisfied in a switching valve of the initially named kind in that a closure element is arranged between the valve plate and the opening of the flow passage and closes the latter when the valve plate is located in its closure position.
In the switching valve in accordance with the invention the opening of the flow passage is closed off by the separate closure element which is provided between the valve plate and the opening of the flow passage. If the valve plate is moved into the opening position, the closure element lies in contact at the opening of the flow passage without a bias force so that the fluid can flow past the closure element out of or into the flow passage respectively. If the valve plate is again moved into its closure position, it takes along with it the closure element, which in turn aligns itself at the opening of the flow passage and closes off the latter as soon as the valve plate has arrived at its final closure position. Since the closure element can move relative to the valve plate, an exact guiding and positioning of the valve plate relative to the opening of the flow passage is no longer required, so that both the valve plate and the guide for the valve plate need to be manufactured less precisely than in the known switching valves. At the same time it is achieved through the freedom of movement of the closure element relative to the opening of the flow passage that the closure element is moved by the inflowing or outflowing fluid respectively into a position in which it lies uniformly in contact at the opening and correctly seals off the latter as soon as it is pressed by the valve plate against the opening and closes off the latter.
Advantageous further developments of the invention can be taken from the description, from the drawings and from the subordinate claims.
Thus it is particularly advantageous to use a valve ball as a closure element which lies in contact at the opening in the shape of a line through its ball shape in every position relative to the opening of the flow passage.
In order that the closure element is also held in a definite position relative to the opening of the flow passage when the valve plate is in its opening position, the valve plate preferably has a recess for the closure element which is aligned with the opening of the flow passage. In order to hold the closure element better in the recess and the opening it is further proposed to form the recess and/or the opening conically. The depth of the opening is greater than the stroke of the valve plate. The closure element, for example a ball, is thereby held in the opening. At the same time the closure element can move parallel to the valve plate in the opening so that it can center itself in the opening. Through the conical cross-sectional form of the recess or of the opening respectively it is achieved that the closure element lies uniformly in contact at the wall of the recess and is held in a definite position. A conical recess and an opening which is provided with a conical sealing surface is suitable in particular in the use of a valve ball as closure element, which, as a result of its surface curvature, conforms particularly well to the walls of the recess and of the opening, which extend at an inclination.
In a particularly preferred embodiment of the switching valve in accordance with the invention, resilient elements which are secured at the valve plate and which guide the latter are provided at the inner surface of the work space which faces the flow passage so that a dislocation of the valve plate transversely to its direction of movement is prevented. Through the resilient elements the valve plate is held in a definite position without it being necessary for the valve plate to be guided precisely.
The valve plate is preferably held in its closure position by a compression spring and is moved by means of an actuator into its opening position, since it is thus ensured that the switching valve remains closed in the event of a dropout of the actuator.
In a preferred embodiment of the switching valve in accordance with the invention the work space is bounded by a one or more piece valve body, a ring which lies in contact at the valve body and a disc which lies in contact at the latter. Through the choice of the material thickness of the disc, when a magnet is used as an actuator, the holding force of the magnet can be influenced if the latter is arranged at the surface of the disc which faces away from valve plate since the material thickness of the disc determines the distance of the valve disc from or the air gap of the valve disc to the magnet respectively.
The geometry of the valve body is preferably dimensioned in such a manner that the valve plate lies sealingly in its closure position at the closure element which projects out of the passage opening when it closes off the opening of the flow passage, without however lying in contact at the valve body, so that a gap remains between the valve plate and the valve body. Through this it is ensured that the entire closure force of the valve plate is transmitted exclusively to the closure element, through which a particularly good sealing action can be achieved. Moreover, in the closure movement of the valve plate the fluid must be forwarded out of the gap between the valve plate and the valve body, through which the closure movement of the valve plate is slightly braked and possibly arising oscillatory movements of the valve plate, which arise after the impact onto the closure element through a resilient rebound of the valve plate, are damped.
The above described switching valve can be used in particular in an injection valve for the fuel injection in an internal combustion engine. In this the flow passage is in connection with a needle guide in which a nozzle needle for the closing off of the injection nozzle of the injection valve is displaceably accommodated.